1. Field of the Invention
This invention pertains generally to measurement of hydraulic features, and more particularly to measurement of the characteristics of hydraulic features in rivers and streams.
2. Description of Related Art
Water flows in rivers and streams are influenced by many hydraulic features including waterfalls, channel steps, knickpoints, weirs, spillways, dams and hydraulic jumps. Hydraulic jumps, for example, are turbulent mixtures of air and water that flow upward, such as downstream of a waterfall or as a roller in a swift moving river. Only two ingredients are needed for a jump to form-a flow obstruction and appropriate water discharge. Natural boulders, woody debris, alluvial bedforms, and abrupt channel geometry changes are examples of frequently occurring natural flow obstructions in channels. In addition, engineered structures such as weirs, check dams, and spillways can induce hydraulic jumps. Along with a flow obstruction, a hydraulic jump needs a specific water flow. If discharge is too low, water will flow around the obstruction. If discharge is too high, excessive water depth will drown the jump.
In this example of a hydraulic feature, naturally occurring hydraulic jumps, are very important because they induce rapid channel change by focusing energy in highly localized portions of the river. This results in oxygenation through their turbulent air-water mixing, habitat for some aquatic organisms, and a natural stressor for other aquatic organisms.
Scientists have a need to assess the internal structure and dynamics of naturally-occurring hydraulic features, and their role in geomorphic channel processes, sediment transport, basin evolution, water quality, and effect on the aquatic food web. Past research on hydraulic features has focused on the effect of dams and weirs and, to a small extent, their risk to unaware swimmers. Fluid mechanics of natural hydraulic features are an important factor in fluvial geomorphology, water quality, and aquatic ecology. For example, significant differences between idealized and natural hydraulic features constrain direct application of traditional fluid dynamics to engineered structures designed to duplicate natural hydraulic features. However, detailed measurements of the characteristics of a natural hydraulic feature can be used to formulate fluid mechanics equations to compute mass, momentum, and energy fluxes as well as provide multivariate statistical data to analyze and classify hydraulic features according to their hydrodynamic structure and function. With accurate measurements, formulated models can be applied to create complex dynamic flow models of natural hydraulic features and thereby construct and deploy effective hydraulic structures to incite channel change and revitalize altered and damaged riparian ecosystems.
The primary characteristics to measure in natural hydraulic features are channel topography, water surface topography, air-water mixing, velocity pressure differentials, and lift and drag forces. Measurement of these characteristics have been accomplished downstream of some dams and weirs where water releases are regulated and access from the dam structure, bridges or improved shorelines is easily obtained. However most natural hydraulic features, hydraulic jumps for example, are in inaccessible locations for vehicles or boats and are in highly unwadable rivers and streams. Rugged terrain around many mountain rivers necessitate portable equipment that can be carried by hand or in a raft. Additionally, uneven ground, deep pools, strong currents and turbulent conditions present in and around natural hydraulic features prevent safe wading, floating or swimming to collect measurements. Wading is typically constrained to velocities approaching 1.5 m/s and depths approaching 1.5 m. Cold water, algal biofilms, and poor subsurface visibility further constrain human stability in high velocity zones. As a result, attempted field investigations have been restricted to sites that are shallow, slow or accessible by a vehicle.
Portable measuring and monitoring equipment and methods to make accurate measurements of the characteristics of natural hydraulic features in rivers and streams are needed.